Frog Fractions creator Jim Crawford gave a presentation titled Preserving a Sense of Discovery in the Age of Spoilers. You can watch it here, or read a transcript here. He recommends several games that illustrate his rules of game design. My favorite example:

In the tabletop RPG Legend of the Five Rings, there’s a sourcebook called “Merchant’s Guide to Rokugan.” If you open it up, there’s a couple pages of merchant’s guide in there, and then it actually turns out to be a manual for the underground network of agents trying to overthrow the government. Which is a legitimately awesome secret unless you really were interested in roleplaying a merchant. Those players hated it.